使用另一个IDisposable实现IDisposable的对象 [英] Objects implementing IDisposable using another IDisposable

问题描述

我尝试用C#开发应用程序，并对MailMessage对象有一些担忧:

I try to develop an application in C# and have some concerns with MailMessage object:

它实现了IDisposable接口，所以我在using语句中使用它.因此，它在之后隐式调用Dispose方法.现在，使用该对象，我需要添加附件，这些附件已转换为byte[]对象，然后将它们添加为流.这是代码的一部分，具有更好的视图:

it implements IDisposable interface, so I use it within using statement. So it implicitly calls Dispose method after. Now, using that object I need to add attachments, which I have converted to byte[] object and I add them as stream. Here's part of code to have better view:

using(MailMessage message = new MailMessage("[e-mail]"){
    MemoryStream stream;
    //here I pass byte array to the stream and create an attachemnt
    message.Attachments.Add(new Attachment(stream, "name.xyz"));

    using(SmtpClient client = new SmtpClient("server.com", port))
    {
        // send message
    }
}

现在，我有一个不受管理的资源:Stream对象.设置附件后，我无法立即关闭它(因此无法调用Dispose方法)，因为在发送消息时会出现错误，因为它在发送时会使用流.

Now, I have one resource unmanaged: Stream object. I can't close it (so can't call Dispose method) right after setting attachments, because I'd get an error when sending message, because it uses the stream while sending.

因此，我需要稍后删除它，我在发送后会这样做.那是第二个using中的代码:

So, I need to get rid of it later, which I do after sending. That's the code in second using:

try
{
    client.Send(messgae);
}
finally
{
    if(stream != null)
        stream.Dispose();
}

现在出现问题:MailMesssage的Dispose方法释放该对象使用的所有资源.我的Stream对象是资源之一，不是吗?因此，当using(MailMessage...终止时，它还应该管理我的Stream对象，不是吗?因此，我不需要手动处置Stream对象.

Now the question: Dispose method of MailMesssage frees all resources used by that object. My Stream object is one of the resources, isn't it? So, when using(MailMessage... terminates it should manage also my Stream object, shouldn't it? So I wouldn't need to dispose of my Stream object manually.

建议的方法:

using(MailMessage message = new MailMessage("[e-mail]"){
    using(MemoryStream stream = ...)
    {
        //here I pass byte array to the stream and create an attachemnt
        message.Attachments.Add(new Attachment(stream, "name.xyz"));

        using(SmtpClient client = new SmtpClient("server.com", port))
        {
            // send message
        }
    }
}

但是问题仍然存在:MailMessage使用此Stream-那么，我们仍然需要自己管理Stream吗?

But the questions stays: MailMessage uses this Stream - so, do we still need to manage Stream on our own?

推荐答案

从参考文档开始，您无需使用using.

From the reference documentation you don't need to when you are using using.

邮件消息处理附件集合，然后进行处置所有附件.

Mail Message disposes Attachment Collection, which then disposes all its attachements.

关于我们应该采用还是依靠这种方法，那么我完全同意佐哈尔的观点

Regarding, should we take or rely on this approach then I totally agree with Zohar on

应该通过显式调用Dispose或使用using语句在代码中表示对IDisposable的处理.

Disposing of an IDisposable should be expressed in your code, either by calling Dispose explicitly or with the using statement.

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